A study of the biological function of basonuclin. The ability to increase ribosome production is essential for cellular proliferation. This is particularly true for keratinocyte stem cells since they must divide continuously to maintain the normal homeostasis of the tissue and must be able to increase the rate of division in response to injury. Basonuclin, a zinc finger protein of 120 kDa, is likely to be a transcriptional regulator that enhances transcription of ribosomal RNA from a basal level. Basonuclin differs from the previously described rRNA transcription factors because its expression is cell type-specific and proliferation-related. Our hypothesis is that regulation of basonuclin affects rRNA transcription and ribosome production in keratinocytes and this regulation is important in maintaining the proliferative ability of keratinocytes. To test this hypothesis, we propose the following three specific aims: Specific Aim 1, We will investigate, by systematic mutagenesis and a co-transfection assay, the sequence (s) in the promoter of rRNA gene that is required for the action of basonuclin. We will also use mutagenesis to define the protein domains that are important for the function of basonuclin as an rRNA transcriptional activator. Specific Aim 2, In addition to ribosomal RNA genes, basonuclin may regulate another group of genes. We hypothesize that this second group includes genes encoding ribosomal proteins. We will test this hypothesis by determining if basonuclin interacts with the promoters of ribosomal protein genes and if it affects their transcription. Specific Aim 3, We will construct transgenic mice that express a dominant-negative mutation of basonuclin in the basal keratinocytes. We will examine if this mutant can inhibit Poll transcription in the basal keratinocytes in vivo and what are the effects of this inhibition on the normal development and maintenance of the epidermis.